1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and more particularly to a photoelectric conversion apparatus having a photoelectric conversion unit that performs photoelectric conversion.
2. Description of the Related Art
An image pickup system generally comprises an auto-focusing (AF) sensor that detects focus.
In Japanese Patent Laid-Open No. 2000-078472, a photoelectric conversion apparatus is described that includes a differential amplification unit that amplifies a signal based on an electric charge generated by a photodiode, a capacitor that holds the signal amplified by the differential amplification unit, and a source follower circuit that transmits the signal held in the capacitor to a subsequent stage. It is proposed that, by feeding the output of the source follower circuit back to the differential amplification unit, benefits can be produced in, for example, reduction of fixed pattern noise (FPN) and improvement of gain.
In Japanese Patent Laid-Open No. 2006-220684, an AF apparatus is described in which a frame memory that stores accumulated signals corresponding to regions of a line sensor obtained when the line sensor is divided into a plurality of regions and a frame memory that stores accumulated signals corresponding to all the regions of the line sensor are included. According to Japanese Patent Laid-Open No. 2006-220684, high-speed AF can be performed even if the amount of defocus is large.
With the techniques disclosed in Japanese Patent Laid-Open No. 2000-078472 and Japanese Patent Laid-Open No. 2006-220684, however, it has been difficult to realize both high-speed AF and high-accuracy AF without increasing the scale of a circuit.